The Sumi is a rare and precious flower known only to the members of the Hisomu Clan. The flower's black petals can be distilled into ink, and its powerful toxins used to create ability-enhancing tattoos known as the Mark.
Sumi grows in the desolated city of Tabriz, a place crawling with bandits. A merchant told Tetsuji about the Sumi and he used it to become young. However, he become maddened by the killings and died under the flying ravens. After this incident, the Hisomu Clan use the Sumi to protect themselves. The Sumi are usually used by the younger members of the clans so that the master can control the madness. 50 years prior to the events of the game, the Hisomu Clan and the bandits made an agreement wherein the ninja would protect the bandits' 'exports' and in return, the bandits would protect the flowers. Eventually the bandits realised the potential of the flowers and turned their backs on the agreement. In retribution, the clan sent Dosan to deal with the situation. Eventually, with no one to tend to the flowers and with multiple factions seeking to exploit the plant, the Sumi's numbers withered away, causing Azai to grow concerned that the Hisomu would disappear as well. By this time, most of the Sumi ink which the clan possessed was stale and dry, which Dosan noticed when he utilized the ink in his tattooing of the Marked Ninja, who became the last to receive the mark, with all its blessings and curses.